Emily S. Howard

Broadband Optical Observations of BL Lacertae during the 1997 Outburst

We present BVRI observations of BL Lacertae during its recent outburst. These observations, made during a 3 month period, cover a significant portion of the optical flare. The reduced data are displayed as light curves and broadband spectra. Changes in the spectral index are analyzed, and the results are compared with previous BL Lac observations. We find that the variations are simultaneous in the optical bands, but the higher frequency bands show a higher amplitude of variability. The spectral index is variable during the active period, and there is marginal evidence that the spectrum flattens as the source gets brighter.

The 1997 Outburst of AO 0235+164: Evidence for a Microlensing Event?

We present multiwavelength observations of AO 0235+164 made during a 5 mag outburst in 1997. Detection of the outburst at the observatory of the South Eastern Association for Research in Astronomy prompted a concerted effort by several observatories to monitor the source in the R band. We present V-, R-, and I-band photometry, as well as contemporaneous 850 μm and X-ray measurements. We also use radio measurements from the University of Michigans World Wide Web site in our analysis. We find that the source varies nearly simultaneously over 6 decades in frequency during this outburst and examine the possibility that the outburst was a result of a microlensing event. The duration of the outburst was on the order of 800 days, and the maximum luminosity was approximately 9.86 × 1047 ergs s-1 (assuming no relativistic beaming). We also analyze the long-term optical light curve and find that, although there is still no evidence for periodicity, the variations are interesting: the timescales between pairs of outbursts are remarkably similar. We suggest that the multifrequency behavior of the 1997 outburst is consistent with microlensing scenarios, while observations of previous outbursts suggest they were not consistent with gravitational microlensing.

Microvariability and Long-Term Variability of Four Blazars

Long-term light curves of four blazars, Mrk 421, Mrk 501, 3C 345, and BL Lacertae were constructed using archival data and supplemented with new observations. The occurrences of microvariability are correlated temporally with long-term optical activity in the light curves. Although the statistics are not conclusive, we find evidence that microvariability is correlated with rapid flux changes rather than specific flux levels. We discuss the implications of these results for quasar variability models.

Gravitational Microlensing and Blazar Variability: The Case of AO 0235+164

We review the basics of gravitational lens phenomena in astrophysics, concentrating on its applicability to Blazar variability. A brief discussion of gravitational lenses in the context of AGN is presented, followed by a more detailed model to explain the high amplitude outburst observed in Blazar AO 0235+164. We find some preliminary model parameters for the 1997–98 outburst of AO 0235+164.